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SubjectRe: [PATCH v5 4/8] hugetlb: perform vmemmap restoration on a list of pages
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On 2023/9/25 08:39, Mike Kravetz wrote:
> The routine update_and_free_pages_bulk already performs vmemmap
> restoration on the list of hugetlb pages in a separate step. In
> preparation for more functionality to be added in this step, create a
> new routine hugetlb_vmemmap_restore_folios() that will restore
> vmemmap for a list of folios.
>
> This new routine must provide sufficient feedback about errors and
> actual restoration performed so that update_and_free_pages_bulk can
> perform optimally.
>
> Special care must be taken when encountering an error from
> hugetlb_vmemmap_restore_folios. We want to continue making as much
> forward progress as possible. A new routine bulk_vmemmap_restore_error
> handles this specific situation.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> mm/hugetlb.c | 98 +++++++++++++++++++++++++++++++-------------
> mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
> mm/hugetlb_vmemmap.h | 10 +++++
> 3 files changed, 118 insertions(+), 28 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index da0ebd370b5f..53df35fbc3f2 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1834,50 +1834,92 @@ static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio,
> schedule_work(&free_hpage_work);
> }
>
> -static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
> +static void bulk_vmemmap_restore_error(struct hstate *h,
> + struct list_head *folio_list,
> + struct list_head *non_hvo_folios)
> {
> struct folio *folio, *t_folio;
> - bool clear_dtor = false;
>
> - /*
> - * First allocate required vmemmmap (if necessary) for all folios on
> - * list. If vmemmap can not be allocated, we can not free folio to
> - * lower level allocator, so add back as hugetlb surplus page.
> - * add_hugetlb_folio() removes the page from THIS list.
> - * Use clear_dtor to note if vmemmap was successfully allocated for
> - * ANY page on the list.
> - */
> - list_for_each_entry_safe(folio, t_folio, list, lru) {
> - if (folio_test_hugetlb_vmemmap_optimized(folio)) {
> + if (!list_empty(non_hvo_folios)) {
> + /*
> + * Free any restored hugetlb pages so that restore of the
> + * entire list can be retried.
> + * The idea is that in the common case of ENOMEM errors freeing
> + * hugetlb pages with vmemmap we will free up memory so that we
> + * can allocate vmemmap for more hugetlb pages.
> + */
> + list_for_each_entry_safe(folio, t_folio, non_hvo_folios, lru) {
> + list_del(&folio->lru);
> + spin_lock_irq(&hugetlb_lock);
> + __clear_hugetlb_destructor(h, folio);
> + spin_unlock_irq(&hugetlb_lock);
> + update_and_free_hugetlb_folio(h, folio, false);
> + cond_resched();
> + }
> + } else {
> + /*
> + * In the case where there are no folios which can be
> + * immediately freed, we loop through the list trying to restore
> + * vmemmap individually in the hope that someone elsewhere may
> + * have done something to cause success (such as freeing some
> + * memory). If unable to restore a hugetlb page, the hugetlb
> + * page is made a surplus page and removed from the list.
> + * If are able to restore vmemmap and free one hugetlb page, we
> + * quit processing the list to retry the bulk operation.
> + */
> + list_for_each_entry_safe(folio, t_folio, folio_list, lru)
> if (hugetlb_vmemmap_restore(h, &folio->page)) {

IIUC, the folio should be deleted from the folio list since this
huge page will be added to the free list (the list is corrupted),
right?

> spin_lock_irq(&hugetlb_lock);
> add_hugetlb_folio(h, folio, true);
> spin_unlock_irq(&hugetlb_lock);
> - } else
> - clear_dtor = true;
> - }
> + } else {
> + list_del(&folio->lru);
> + spin_lock_irq(&hugetlb_lock);
> + __clear_hugetlb_destructor(h, folio);
> + spin_unlock_irq(&hugetlb_lock);
> + update_and_free_hugetlb_folio(h, folio, false);
> + cond_resched();
> + break;
> + }
> }
> +}
> +
> +static void update_and_free_pages_bulk(struct hstate *h,
> + struct list_head *folio_list)
> +{
> + long ret;
> + struct folio *folio, *t_folio;
> + LIST_HEAD(non_hvo_folios);
>
> /*
> - * If vmemmmap allocation was performed on any folio above, take lock
> - * to clear destructor of all folios on list. This avoids the need to
> - * lock/unlock for each individual folio.
> - * The assumption is vmemmap allocation was performed on all or none
> - * of the folios on the list. This is true expect in VERY rare cases.
> + * First allocate required vmemmmap (if necessary) for all folios.
> + * Carefully handle errors and free up any available hugetlb pages
> + * in an effort to make forward progress.
> */
> - if (clear_dtor) {
> +retry:
> + ret = hugetlb_vmemmap_restore_folios(h, folio_list, &non_hvo_folios);
> + if (ret < 0) {
> + bulk_vmemmap_restore_error(h, folio_list, &non_hvo_folios);
> + goto retry;
> + }
> +
> + /*
> + * At this point, list should be empty, ret should be >= 0 and there
> + * should only be pages on the non_hvo_folios list.
> + * Do note that the non_hvo_folios list could be empty.
> + * Without HVO enabled, ret will be 0 and there is no need to call
> + * __clear_hugetlb_destructor as this was done previously.
> + */
> + VM_WARN_ON(!list_empty(folio_list));
> + VM_WARN_ON(ret < 0);
> + if (!list_empty(&non_hvo_folios) && ret) {
> spin_lock_irq(&hugetlb_lock);
> - list_for_each_entry(folio, list, lru)
> + list_for_each_entry(folio, &non_hvo_folios, lru)
> __clear_hugetlb_destructor(h, folio);
> spin_unlock_irq(&hugetlb_lock);
> }
>
> - /*
> - * Free folios back to low level allocators. vmemmap and destructors
> - * were taken care of above, so update_and_free_hugetlb_folio will
> - * not need to take hugetlb lock.
> - */
> - list_for_each_entry_safe(folio, t_folio, list, lru) {
> + list_for_each_entry_safe(folio, t_folio, &non_hvo_folios, lru) {
> update_and_free_hugetlb_folio(h, folio, false);
> cond_resched();
> }
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 4558b814ffab..77f44b81ff01 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -480,6 +480,44 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
> return ret;
> }
>
> +/**
> + * hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
> + * @h: hstate.
> + * @folio_list: list of folios.
> + * @non_hvo_folios: Output list of folios for which vmemmap exists.
> + *
> + * Return: number of folios for which vmemmap was restored, or an error code
> + * if an error was encountered restoring vmemmap for a folio.
> + * Folios that have vmemmap are moved to the non_hvo_folios
> + * list. Processing of entries stops when the first error is
> + * encountered. The folio that experienced the error and all
> + * non-processed folios will remain on folio_list.
> + */
> +long hugetlb_vmemmap_restore_folios(const struct hstate *h,
> + struct list_head *folio_list,
> + struct list_head *non_hvo_folios)
> +{
> + struct folio *folio, *t_folio;
> + long restored = 0;
> + long ret = 0;
> +
> + list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
> + if (folio_test_hugetlb_vmemmap_optimized(folio)) {
> + ret = hugetlb_vmemmap_restore(h, &folio->page);
> + if (ret)
> + break;
> + restored++;
> + }
> +
> + /* Add non-optimized folios to output list */
> + list_move(&folio->lru, non_hvo_folios);
> + }
> +
> + if (!ret)
> + ret = restored;
> + return ret;
> +}
> +
> /* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
> static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
> {
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index c512e388dbb4..0b7710f90e38 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -19,6 +19,9 @@
>
> #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head);
> +long hugetlb_vmemmap_restore_folios(const struct hstate *h,
> + struct list_head *folio_list,
> + struct list_head *non_hvo_folios);
> void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head);
> void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list);
>
> @@ -45,6 +48,13 @@ static inline int hugetlb_vmemmap_restore(const struct hstate *h, struct page *h
> return 0;
> }
>
> +static long hugetlb_vmemmap_restore_folios(const struct hstate *h,
> + struct list_head *folio_list,
> + struct list_head *non_hvo_folios)
> +{
> + return 0;
> +}
> +
> static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> {
> }

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